This invention relates to control arrangements for controlling the size of a gap between first and second components. More particularly, but not exclusively, the invention relates to control arrangements for controlling the size of a gap between rotating and static components in a gas turbine engine.
Turbines and compressors in gas turbine engines have components which rotate at relatively high speeds and which are exposed to pressurised gases. Gaps are defined between the rotating and static components, and these are required to be as small as possible in order to minimise the leakage of the gases. The degree of leakage can have a significant effect on the overall efficiency of a gas turbine engine. Various ways have been proposed for minimising the leakage through the gaps, for example by the use of materials with different coefficients of thermal expansion, or by the use of seals, for example labyrinth seals, abradable seals, brush seals, or leaf seals.
According to one aspect of this invention, there is provided a control arrangement for controlling the size of a gap between first and second components, the control arrangement comprising first magnet means on the first component, and second magnet means on the second component, the first and second magnet means being in magnetic interaction with each other across the gap, and the arrangement further including control means in operative association with the first magnet means to control the size of the gap, wherein variations in magnetic flux across the gap cause the first magnet means to cause the control means to effect relative movement of the first and second components to vary the size of the gap.
Preferably, the first magnet means is moveable in a first direction to cause the control means to effect relative movement of the first and second components to increase the gap and in a second direction to cause the control means to effect relative movement of the first and second components to decrease the gap, the first and second magnet means being so arranged that relative movement of the first and second components towards each other moves the first magnet means in the first direction, and relative movement of the first and second components away from each other moves the first magnet means in the second direction.
The phrase xe2x80x9cmagnet meansxe2x80x9d as used herein is intended to cover the situation where the magnet means comprises either a magnet, or an electrically conductive material in which a magnetic field can be established on changes in magnetic flux therethrough.
The first magnet means may include biasing means to bias the first magnet means in the second direction. The biasing means may comprise resilient urging means, for example, a spring.
Each of the first and second magnet means may comprise a magnet or magnetic material. The magnets may be permanent magnets. Alternatively, one of the first and second magnet means may comprise a magnet or magnetic material and the other of the first and second magnet means may comprise an electrically conductive material, whereby movement of the first and second magnet means relative to each other establishes a magnetic field in the electrically conductive material. Preferably, the first magnet means compresses a magnet or magnetic material and the second magnet means comprises an electrically conductive material.
In a first embodiment, the first and second magnet means are arranged such that they move transversely relative to each other and they may be arranged to repel each other. In a second embodiment, the first and second magnet means are arranged such that, on relative movement of said first and second components transverse to the gap, a force is applied to at least one of said first and second magnet means generally parallel, or generally tangential, to the direction of said relative movement.
This invention is particularly suitable for use in rotary apparatus for gas turbine engines, for example in the turbine and compressor sections of such engines. Such rotary apparatus typically includes a rotor, for example turbine or compressor rotor blades, and a stator, for example stator vanes, nozzle guide vanes, and a casing, wherein the rotor rotates relative to the stator. In such apparatus, one of the first and second magnet means is provided on the stator means, and the other of the first and second magnet means is provided on the rotor means. Conveniently, the first magnet means is provided on the stator means, and the second magnet means is provided on the rotor means. Where the second magnet means is an electrically conductive material, the second magnet means may comprise at least some of the material from which the rotor or stator means is formed. Alternatively, the electrically conductive material may be separate electrically conductive members incorporated into the rotor or stator means.
The second component preferably comprises a rotor carrying a plurality of rotor blades. In one embodiment, the first component forms part of a stator casing, the first magnet means being provided on the stator casing, and the second magnet means being provided at the radially outer ends of the rotor blades. In another embodiment, the first component forms part of a stator vane, the first magnet means being provided at a radially inner end of each stator vane, and the second magnet means is provided on the rotor.
The first magnet means may be pivotally mounted to the first component. The first magnet means may be in the form of a magnetic yoke, and the second magnet means may comprise a protrusion extending between the arms of the yoke. The control means in this embodiment may be in the form of a valve to control the flow of fluid in or out of a chamber.
In one embodiment, the control means may be a pneumatic or an hydraulic control means, which may include a chamber to receive a force transmission fluid, one wall of the chamber constituting the first component and the chamber having at least one inlet means through which the fluid can pass. Preferably, the first magnet means is moveable to open or close the inlet means. The chamber may also be provided with outlet means through which the fluid may exit the chamber. Thus, in this embodiment, changes of pressure in the chamber can move the first component towards or away from the second component.
In another embodiment, the control means may comprise a thermo-deformable member and temperature control means for heating and cooling the thermo-deformable member, movement of the first magnet means, causing the temperature control means to either heat or cool the thermo-deformable member, to deform said member to effect relative movement of the first and second components to decrease or increase the gap.
The temperature control means may comprise conduits connected in fluid communication with respective supplies of hot and cold fluid, such as a gas. In this embodiment, the first magnet means may be connected to a valve means to control the flow of hot and cold fluid onto the thermo-deformable member.
In one embodiment, the thermodeformable member comprises a bi-metallic member. In another embodiment, the thermo-deformable member comprises a shape memory alloy, which may be a one-way shape memory alloy or a two-way shape memory alloy.
Where the thermo-deformable member is a bi-metallic member or a two-way shape memory alloy member, heating or cooling the bi-metallic or the shape memory alloy member causes said member to deform to effect relative movement of the first and second components to increase or decrease the gap and respective cooling or heating the bi-metallic or shape memory alloy member causes said member to deform to effect relative movement of the first and second components in the opposite direction.
Where the thermo-deformable member is a one-way shape member alloy member, heating or cooling the member causes the member to deform to effect relative movement of the first and second components to increase or decrease the gap. This embodiment may further include force applying means to apply a force to the member or the first component to effect relative movement of the first and second components in the opposite direction.
In another embodiment, which is suitable for use in controlling the gap between a second component in the form of fan blades of a gas turbine engine, and a first component in the form of a casing surrounding the fan blades, the control means comprises a chamber defined in the first component having resiliently deformable side walls, whereby the side walls urge a radially inner wall of the chamber towards or away from the second component. The chamber is preferably in fluid communication with a supply of a force transmission fluid to urge the radially inner wall in the opposite direction away from or towards the second component. Preferably, the side walls urge the radially inner wall away from the second component and the force transmission fluid urges the radially inner wall towards the second component.
The first magnet means may be arranged over an aperture in the chamber to control the flow of said fluid into or out of the chamber. The second magnet means may be provided on the second component, whereby as the gap between the first and second magnet means increases the first magnet means moves to open or close the aperture, thereby controlling the flow of fluid into the chamber to effect relative movement of the first and second components to decrease the gap, and as the gap between the first and second magnet means decreases the first magnet means may move in the opposite direction to close or open the aperture thereby controlling the flow of fluid into the chamber and increasing the gap.